Fumarate as positive modulator of allosteric transitions in the pentameric ligand-gated ion channel GLIC: Requirement of an intact vestibular pocket.

Catherine van Renterghem (1) , Ákos Nemecz (1) , Sandrine Delarue-Cochin (2) , Delphine Joseph (2) , Pierre‐Jean Corringer (1)

1 Récepteurs Canaux - Channel Receptors
2 BioCIS - Biomolécules : Conception, Isolement, Synthèse

GLIC is a prokaryotic orthologue of brain pentameric neurotransmitter receptors. Using whole-cell patch-clamp electrophysiology in a host cell line, we show that short-chain di-carboxylate compounds are positive modulators of pHo 5-evoked GLIC activity, with a rank order of action fumarate > succinate > malonate > glutarate. Potentiation by fumarate depends on intracellular pH, mainly as a result of a strong decrease of the pHo 5-evoked current when intracellular pH decreases. The modulating effect of fumarate also depends on extracellular pH, as fumarate is a weak inhibitor at pHo 6 and shows no agonist action at neutral pHo. A mutational analysis of residue-dependency for succinate and fumarate effects, based on two carboxylate-binding pockets previously identified by crystallography (Fourati et al. 2020), shows that positive modulation involves both the inter-subunit pocket, homologous to the neurotransmitter-binding orthotopic site, and the intra-subunit (also called vestibular) pocket. An almost similar pattern of mutational impact is observed for the effect of caffeate, a known negative modulator. We propose, for both di- carboxylate compounds and caffeate, a model where the inter-subunit pocket is the actual binding site, and the region corresponding to the vestibular pocket is required either for inter-subunit binding itself, or for binding-to-gating coupling during the allosteric transitions involved in pore gating modulation.

Mots clés: pLGIC; GLIC; fumarate; succinate; ligand-gated ion channel; positive allosteric modulator; orthosteric site; orthotopic site; allotopic site; vestibular site; intracellular pH

Domaines: Chimie

Catherine van Renterghem, Ákos Nemecz, Sandrine Delarue-Cochin, Delphine Joseph, Pierre‐Jean Corringer. Fumarate as positive modulator of allosteric transitions in the pentameric ligand-gated ion channel GLIC: Requirement of an intact vestibular pocket.: Fumarate as positive allosteric modulator of GLIC.. The Journal of Physiology, inPress, ⟨10.1113/JP283765⟩. ⟨pasteur-04093140⟩